1. Field of the Invention
The present invention relates to a variable geometry cylinder mirror and more particularly to a highly configurable, high precision cylindrically deformable variable geometry mirror.
2. Description of the Related Art
In the field of high-precision micro optical systems such as an optical pickup, a micro variable focus mirror capable of changing the curvature of its reflecting face has been proposed so as to aim at simplification of the structure for focusing, which conventionally uses an electromagnetic actuator.
Further, in a small image pickup optical system, miniaturization is largely dependant on the size of the variable focus mirror.
Adoption of micro electromechanical system (MEMS) technology in a variable focus mirror enables low-cost, high-precision manufacturing thereof.
An example of the cylindrically deformable variable geometry cylinder mirror of this technology is a monolithic reflecting mirror apparatus disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2-101402.
In this monolithic reflection mirror unit, as shown in FIG. 26, a metallic thin film 54, which serves as an electrode layer, is formed on a silicon semiconductor substrate 51, which acts as a fixed side electrode, through a silicon epitaxial layer 52 and a silicon oxide thin film 53. Window holes 56, 57 are formed in the silicon oxide thin film 53 and the metallic thin film 54 with a central portion 55 left between them.
Because the window holes 56, 57 communicate with each other through a vacant portion 58 formed in the silicon epitaxial layer 52, the central portion 55 is set up as a straddle-mounted type reflection mirror portion.
The straddle-mounted type reflection mirror portion 55 opposes the silicon semiconductor substrate 51 through the vacant portion 58. By applying a potential difference to 51 and 55, the reflection mirror portion 55 is distorted, thereby functioning as a variable geometry cylinder mirror.
However, although the variable geometry cylinder mirror employing the conventional monolithic type reflection mirror unit can be so constructed as a small, low-cost variable geometry cylinder mirror, the electrostatic force applied to the reflection mirror portion cannot be changed according to each position. Thus, this variable geometry cylinder mirror cannot be deformed to an asymmetrical shape.
Further, the variable geometry cylinder mirror using the conventional monolithic type reflection mirror unit can only be changed from a flat face to a concave face and it cannot be deformed to a convex shape.
Additionally, because the center of the reflection mirror portion always drops with deformation of the variable geometry cylinder mirror using the conventional monolithic type reflection mirror unit, there is a problem that the curvature cannot be changed with the center portion fixed.
Further, the straddle mounted type structure is distorted by deformation of the reflection mirror portion. Thus, if a large distortion is desired, a high voltage is needed in order to produce a large electrostatic force.
The present invention has been achieved in view of the above-described problems and therefore, an object of the present invention is to provide a small variable geometry cylinder mirror, the shape of which can be freely set and can also be asymmetrical.
Another object of the present invention is to provide a variable geometry cylinder mirror, which can be deformed continuously from a concave face to a convex face and further which can be deformed with the center or any point of the reflection mirror fixed.
Still another object of the present invention is to provide a variable geometry cylinder mirror capable of obtaining large changes in curvature with a relatively low voltage.
In order achieve the above objects, according to a first aspect of the present invention, there is provided a variable geometry cylinder mirror comprising:
a frame member;
a flexible thin film in which two end portions opposing each other are supported by the frame member;
a reflection surface which is provided on the flexible thin film and reflects light;
a first electrode provided integrally with the flexible thin film;
a second electrode substantially fixed to the frame member so as to oppose the first electrode on an opposite side of the reflection surface; and
a third electrode substantially fixed to the frame member so as to oppose the first electrode on the same side as the reflection surface,
wherein an optical opening to introduce light into the reflection surface is provided on the side of the reflection surface,
at least any one of the second and third electrodes is divided in the direction connecting the two end portions, and
the configuration of the reflection surface is controlled to a desired configuration by applying a desired voltage selectively to between the first electrode and the divided second or third electrode.
According to a second aspect of the present invention, there is provided a variable geometry cylinder mirror according to the first aspect, wherein the reflection surface of the flexible thin film is formed of metallic thin film and serves as the first electrode.
According to a second aspect of the present invention, there is provided a variable geometry cylinder mirror according to first aspect, wherein an openings are provided on both sides of the reflection surface in the flexible member across a straight line connecting the end portions supported by the frame member.
According to a fourth aspect of the present invention, there is provided a variable geometry cylinder mirror according to the first aspect, wherein in a region between the end portion supported by the frame member and the reflection surface in the flexible thin film, stiffness thereof in the direction in which the second or third electrode is divided is decreased.
According to a fifth aspect of the present invention, there is provided a variable geometry cylinder mirror according to the fourth, wherein the region in which the stiffness of the flexible thin film is dropped is wave-like.
According to a sixth aspect of the present invention, there is provided a variable geometry cylinder mirror according to the fifth aspect, wherein the flexible thin film is composed of overlaid layers of metallic thin film and silicon nitride or metallic thin film and silicon oxide.
According to a seventh aspect of the present invention, there is provided a variable geometry cylinder mirror according to the fourth aspect, wherein as for the sectional area of the flexible thin film in a direction perpendicular to the direction in which the second or third electrode is divided, that of the region in which the stiffness of the flexible thin film is dropped is smaller than that of a region corresponding to the reflection surface.
According to an eighth aspect of the present invention, there is provided variable geometry cylinder mirror according to the fourth aspect, wherein an opening or a cutout is provided in the region in which the stiffness of the flexible thin film is dropped.
According to a ninth aspect of the present invention, there is provided a variable geometry cylinder mirror according to the first aspect, wherein the flexible thin film is composed of overlaid layers of metallic thin film and polymer material thin film.
According to a tenth aspect of the present invention, there is provided a variable geometry cylinder mirror according to the seventh aspect, wherein the flexible thin film is composed of overlaid layers of metallic thin film and polymer material thin film.
According to an eleventh of the present invention, there is provided a variable geometry cylinder mirror according to the eighth aspect, wherein the flexible thin film is composed of overlaid layers of metallic thin film and polymer material thin film.
According to a twelfth aspect of the present invention, there is provided a variable geometry cylinder mirror according to the first aspect, wherein the third electrode and a supporting member thereof are provided outside the optical opening.
According to a thirteenth aspect of the present invention, there is provided a variable geometry cylinder mirror according to the first aspect, wherein the third electrode is disposed within the optical opening while the third electrode disposed within the optical opening and the supporting member thereof have property allowing light to be transmitted through.
According to a fourteenth aspect of the present invention, there is provided a variable geometry cylinder mirror comprising:
a frame member;
a flexible thin film in which two end portions opposing each other are supported by the frame member;
a reflection surface which is provided on the flexible thin film and reflects light;
a first electrode provided integrally with the flexible thin film; and
a second electrode substantially fixed to the frame member so as to oppose the first electrode on an opposite side of the reflection surface, the second electrode being divided in the direction connecting the two end portions,
wherein the configuration of the reflection is controlled to a desired configuration by applying a desired voltage selectively to between the first electrode and the divided second or third electrode.
According to a fifteenth aspect of the present invention, there is provided a variable geometry cylinder mirror according to the fourteenth aspect, wherein the reflection surface of the flexible thin film is formed of metallic thin film and serves as the first electrode.
According to a sixteenth aspect of the present invention, there is provided a variable geometry cylinder mirror according to the fourteenth aspect, wherein an openings are provided on both sides of the reflection surface in the flexible member across a straight line connecting the end portions supported by the frame member.
According to a seventeenth aspect of the present invention, there is provided a variable geometry cylinder mirror according to the fourteenth aspect, wherein in a region between the end portion supported by the frame member and the reflection surface in the flexible thin film, stiffness thereof in the direction in which the second electrode is divided is decreased.
According to an eighteenth aspect of the present invention, there is provided a variable geometry cylinder mirror according to the seventeenth aspect, wherein the region in which the stiffness of the flexible thin film is dropped is wave-like.
According to a nineteenth aspect of the present invention, there is provided a variable geometry cylinder mirror according to the eighteenth aspect, wherein the flexible thin film is composed of overlaid layers of metallic thin film and silicon nitride or metallic thin film and silicon oxide.
According to a twentieth aspect of the present invention, there is provided a variable geometry cylinder mirror according to the seventeenth aspect, wherein as for the sectional area of the flexible thin film in a direction perpendicular to the direction in which the second electrode is divided, that of the region in which the stiffness of the flexible thin film is dropped is smaller than that of a region corresponding to the reflection surface.
According to a twenty-first aspect of the present invention, there is provided a variable geometry cylinder mirror according to the seventeenth aspect, wherein an opening or a cutout is provided in the region in which the stiffness of the flexible thin film is dropped.
According to a twenty-second aspect of the present invention, there is provided a variable geometry cylinder mirror according to the fourteenth aspect, wherein the flexible thin film is composed of overlaid layers of metallic thin film and polymer material thin film.
According to a twenty-third aspect of the present invention, there is provided a variable geometry cylinder mirror according to the twentieth aspect, wherein the flexible thin film is composed of overlaid layers of metallic thin film and polymer material thin film.
According to a twenty-fourth aspect of the present invention, there is provided a variable geometry cylinder mirror according to the twenty-first aspect, wherein the flexible thin film is composed of overlaid layers of metallic thin film and polymer material thin film.
According to a twenty-fifth aspect of the present invention, there is provided a variable geometry cylinder mirror according to the first aspect, wherein the flexible thin film having the frame member, the reflection surface and the first electrode is manufactured by:
a diffused layer forming step of forming a diffused layer having a predetermined shape of a conductive type in a first main face of a mono-crystal silicon substrate of another conductive type;
a thin film laminating step of laminating a thin film on the first main face of the mono-crystal silicon substrate;
an etching step of, with a predetermined voltage applied to the diffused layer of the conductive type, carrying out electrochemical etching from a second main face in etching solution; and
a cutting and separating step of cutting and separating frame-like mono-crystal silicon which is part of the mono-crystal silicon substrate form portions corresponding to the flexible thin film and the frame member.
According to a twenty-sixth aspect of the present invention, there is provided a variable geometry cylinder mirror according to the fourteenth aspect, wherein the flexible thin film having the frame member, the reflection surface and the first electrode is manufactured by:
a diffused layer forming step of forming a diffused layer having a predetermined shape of a conductive type in a first main face of a mono-crystal silicon substrate of another conductive type;
a thin film laminating step of laminating a thin film on the first main face of the mono-crystal silicon substrate;
an etching step of, with a predetermined voltage applied to the diffused layer of the conductive type, carrying out electrochemical etching from a second main face in etching solution; and
cutting and separating step of cutting and separating frame-like mono-crystal silicon which is part of the mono-crystal silicon substrate form portions corresponding to the flexible thin film and the frame member.
According to a twenty-seventh aspect of the present invention, there is provided a variable geometry cylinder mirror according to the fifth aspect, wherein the flexible thin film having the frame member, the reflection surface and the first electrode is manufactured by:
a groove forming step of forming parallel grooves in a first main face of a flat substrate;
a thin film forming step of forming a thin film on the first main face of the substrate;
an etching step of etching until the thin film formed in the thin film forming step is exposed from a second main face of the substrate; and
a cutting and separating step of cutting and separating a fame-like portion which is part of the substrate from portions corresponding to the flexible thin film and the frame member.
According to a twenty-eighth aspect of the present invention, there is provided a variable geometry cylinder mirror according to the eighteenth aspect, wherein the flexible thin film having the frame member, the reflection surface and the first electrode is manufactured by:
a groove forming step of forming parallel grooves in a first main face of a flat substrate;
a thin film forming step of forming a thin film on the first main face of the substrate;
an etching step of etching until the thin film formed in the thin film forming step is exposed from a second main face of the substrate; and
a cutting and separating step of cutting and separating a fame-like portion which is part of the substrate from portions corresponding to the flexible thin film and the frame member.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.